1. Field of the Invention
The present invention relates to a humidifier and, more particularly, to a humidifier used in a pressure support system that includes a valve to prevent a back-flow of fluid from the humidifier into a pressure support device.
2. Description of the Prior Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas to the airway of a patient. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle or a monitored condition of the patient, to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), or congestive heart failure. Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of patient to interface the ventilator or pressure support device with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
It is also desirable in many instances in both invasive and non-invasive ventilation to humidify the flow of gas provided to the patient. To this end, humidification systems have been developed that include a humidification chamber provided in-series with a pressure support device to add moisture to the gas output by the pressure support device. FIG. 1 illustrates an example of a conventional configuration in which a pressure support device 10 having an outlet port 12 supplies pressurized gas to a patient circuit 13, which is an elongated flexible tube. Patient circuit 13 is connected to an inlet port 14 of a humidifier 16. Humidifier 16 includes a humidification chamber 15 that is filled with fluid, typically water or distilled water. An outlet port 18 of humidifier chamber 15 is coupled via patient circuit 20 to a patient interface (not shown), such as a nasal mask. In operation, pressurized gas from pressure support device 10 passes through patient circuit 13 to humidifier 16. The gas interacts with the water in the humidifier chamber and exits into tubing 20 where it is communicated to an airway of a patient. Some conventional humidification systems include a heater operatively coupled to humidifier chamber 15 to facilitate the humidification process.
One reason patient circuit 13 is provided between the humidification chamber and pressure support device 10 is to prevent fluid from flowing from the humidifier back into the pressure support device should the humidifier 16 be tipped over. Water entering pressure support device 10 could damage the device.
It is also known to couple the outlet of pressure support device 10 directly to the inlet of the humidification chamber, as shown, for example, in FIG. 2. In this configuration the humidification chamber is rigidly coupled to the pressure support device. However, this configuration exacerbates the problem of fluid flowing from the humidification chamber back into the pressure support device, because of the direct and close connection between the inlet port of the humidification chamber and the outlet port of the pressure support device.
An attempt to prevent back-flow of water from a humidification chamber in the pressure support device using a snorkel-like inlet to the humidification chamber is disclosed in U.S. Pat. No. 6,398,197. While the snorkel type of configuration taught by this patent may help minimize water from entering the outlet of the pressure support device due to backsplash or tilting of the system, it does not prevent water from entering the pressure support device due to condensation and rainout, i.e., water contained in the gas or vapor that may flow back from the humidification chamber into the pressure support device. In addition, in certain orientations at certain water levels, such as if the pressure support device and humidifier are tilted on their side and the humidification chamber even merely half full, the snorkel configuration of the '197 patent has little or no ability to prevent the back-flow of fluid from the humidification chamber into the pressure support device.